The sticky caliper is most likely just the slide pins rusty or not lubricated - maybe the rubber bellows have split or not fitted properly and letting water in. The piston only pushed the inside pad up to disc, for the outside pad to make proper contact with equal pressure requires the whole body of the caliper to slide on the pins - this normally shows up as a rusty surface or uneven polish on the outside face of the disc. The best way to prevent cylinder / piston problems is to regularly flush the brake fluid and replace the fluid that has absorbed water out of the system.... otherwise the water causes corrosion of the piston or bore, you can get Jazz slide pins online for not much money.
Try 'brakes international' based in Rochdale, they sell Bremtech which are good kit and contains the pins with new caliper bolts pre-coated with threadlock, new rubber gaiters and molybdenum grease sachet .. for about a tenner... ( for one caliper )